Clashes in the southern city of Aden continued late into Sunday, with as many as 100 people now reported killed in the southern capital in the last few days.

As yet unconfirmed reports, published in the Saudi-owned al-Arabiya, also said that forces allied to former Yemeni President Ali Abdullah Saleh had begun approaching the southern capital on Monday.

According to the reports, Saleh’s forces are now a mere 30 kilometres from Aden where the Houthi militias have been clashing with forces loyal to President Abd-Rabbuh Mansour Hadi.

While Hadi loyalists told Al Jazeera they had recaptured the airport, which has changed hands several times in the last few days, the two sides were still fighting in the northern parts of the city, with the Houthis also making a push into central Aden.

Ali Abdullah Saleh has long been rumoured to be supporting the Houthis and has widely been blamed for their ability to overrun vast swathes of Yemen since last year. Saleh over the weekend appealed for the Saudi-led strikes to end and for all sides to return to the negotiating table, but his pleas were rejected by the Arab League.

The Houthi and alleged pro-Saleh advance south to Aden, seen as a Hadi stronghold, have continued despite ongoing airstrikes led by Saudi Arabia that have taken aim at Houthi positions across much of the country.

On the fifth consecutive night of bombing, fighter jets roared in the skies above Sanaa from 9:00 pm local time on Sunday night (1800 GMT) until around dawn.

The strikes were heaviest in the area around Marib, 140 kilometers east of Sanaa, where it hit radar facilities and surface-to-air missile batteries, local officials told AFP.

In western Yemen, anti-aircraft defenses were targeted in the port city of Hodeida, as well as several military positions farther south along the coast, residents said.

Saudi coalition spokesman Brigadier General Ahmed Asseri on Sunday stressed that the airstrikes were making progress.

"We feel that day by day they [the Houthis] lose ... we continue to put the pressure on them to stop them ... We believe the situation around Aden will be better and better, day by day," he said.

The Saudis, who head a 10-member coalition against the Houthis, have also vowed to keep on with airstrikes until Hadi – who fled to Saudi Arabia last week – is fully reinstated.

"We will set the conditions necessary to allow the president [Hadi] and his government to run the country," Asseri said.

"The Yemeni army was almost dismantled (by internal fractures after a 2011 uprising) ... one of the conditions is for them to take over. We will continue to attack the militias, we will keep them under pressure, until the conditions become very favourable for the army to take over.”

Arab League head Nabil el-Araby also said that the airstrikes would continue until the Houthis put down their weapons and withdraw.

"Yemen was on the verge of collapse, which prompted a reaction from Arab states and the international community," Araby said on Sunday.

"The [airstrikes] came after all other means to achieve a peaceful solution ... were exhausted. The [strikes] will continue until the Houthis hand over their weapons."

Hadi has meanwhile continued to keep up the pressure on his Arab allies, urging them to keep bombing until Iran's "puppet" Houthi Shiite militias are defeated.

His Foreign Minister Riyadh Yassin said there could be "no negotiations and dialogue" with the rebels "until the legitimate government has control over all Yemeni lands".